Rechargeable (secondary) batteries are of increasing importance both in the consumer electronics field (as components of e.g. mobile telephones and laptop computers) as well as in vehicle and aerospace applications. An example of a rechargeable battery is the lithium-ion battery in which lithium ions in the electrolyte move from the negative electrode to the positive electrode during discharge (and move in the reverse direction during charging). FIG. 2 shows an example of an electrochemical device used to store energy (a battery) containing a positive electrode material and a negative electrode material separated by separator containing a liquid, gel, polymeric or solid electrolyte, with a current collector used on both sides of the battery to carry the electrical energy.
Organic materials can be used effectively to store charge. Thus, US 2010/0009256 and US 2008/0038636 relate to the use of a polyradical material, a polymer with pendant nitroxyl radical groups, as an electrode active material. US 2003/0096165 discloses materials containing polyradicals of various structures for use in secondary batteries, and U.S. Pat. No. 7,045,248 focuses on boron or sulfur radicals. Such “Organic Radical Batteries” (ORBs) show good performance in that they offer high power density. However, the materials are not electronically conductive, hence to obtain such performance it is needed to add up to 50% of carbon in the electrode formulation. This causes a sharp decrease of both volumetric and gravimetric energy density.
Another example of organic material used for energy storage was presented by researchers in Amiens (Chem Sus Chem DOI: 10.1002/cssc.200700161). These materials provide excellent charge storage (very high capacity) but fall short of the rate capability needed to provide high power density.
Organosulfur compounds (3 Electrochem Soc 2007 154 A844-A848) have been proposed as other organic active materials for energy storage, but their performance is seriously hampered by their solubility in the electrolyte.